Cryocoolers

The last two years have witnessed a continuation in the breakthrough shift toward pulse tube cryocoolers for long-life, high-reliability cryocooler applications. New this year are papers de scribing the development of very large pulse tube cryocoolers to provide up to 1500 watts of cooling for industrial applications such as cooling the superconducting magnets of Mag-lev trains, coolmg superconducting cables for the power mdustry, and liquefymg natural gas. Pulse tube coolers can be driven by several competing compressor technologies. One class of pulse tube coolers is referred to as "Stirling type" because they are based on the linear Oxford Stirling-cooler type compressor; these generally provide coolmg m the 30 to 100 K temperature range and operate ^t frequencies from 30 to 60 Hz. A second type of pulse tube cooler is the so-called "Gifford-McMahon type. " Pulse tube coolers of this type use a G-M type compressor and lower frequency operation (~1 Hz) to achieve temperatures in the 2 to 10 K temperature range. The third type of pulse tube cooler is driven by a thermoacoustic oscillator, a heat engine that functions well in remote environments where electricity is not readily available. All three types are described, and in total, nearly half of this proceedings covers new developments in the pulse tube arena. Complementing the work on low-temperature pulse tube and Gifford-McMahon cryocoolers is substantial continued progress on rare earth regenerator materials.

The last two years have witnessed a continuation in the breakthrough shift toward pulse tube cryocoolers for long-life, high-reliability cryocooler applications. One class of pulse tubes that has reached maturity is referred to as “Stirling type” because they are based on the linear Oxford Stirling-cooler type compressor; these generally provide cooling in the 30 to 100 K temperature range and operate at frequencies from 30 to 60 Hz. The other type of pulse tube cooler making great advances is the so-called “Gifford-McMahon type. ” Pulse tube coolers of this type use a G-M type compressor and lower frequency operation to achieve temperatures in the 2 to 10 K temperature range. Nearly a third of this proceedings covers these new developments in the pulse tube arena. Complementing the work on low-temperature pulse tubes is substantial continued progress on rare earth regenerator materials and Gifford-McMahon coolers. These technologies continue to make great progress in opening up the 2 - 4 K market. Also in the commercial sector, continued interest is being shown in the development of long-life, low-cost cryocoolers for the emerging high temperature superconductor electronics market, particularly the cellular telephone base-station market. At higher temperature levels, closed-cycle J-T or throttle-cycle refrigerators are taking advantage of mixed refrigerant gases to achieve low-cost cryocooler systems in the 65 to 80 K temperature range.

Cryocoolers 10 is the premier archival publication of the latest advances and performance of small cryogenic refrigerators designed to provide localized cooling for military, space, semi-conductor, medical, computing, and high-temperature superconductor cryogenic applications in the 2-200 K temperature range. Composed of papers written by leading engineers and scientists in the field, Cryocoolers 10 reports the most recent advances in cryocooler development, contains extensive performance test results and comparisons, and relates the latest experience in integrating cryocoolers into advanced applications.

This book serves as an introduction to cryocooler technology and describes the principle applications of cryocoolers across a broad range of fields. It covers the specific requirements of these applications, and describes how the advantages and disadvantages of different cryocooler systems are taken into consideration. For example, Stirling coolers tend to be used only in space applications because of their high coefficient of performance, low weight and proven reliability, whilst Gifford-McMahon coolers are used for ground applications, such as in cryopumps and MRI shield cooling applications. Joule-Thomson cryocoolers are used in missile technology because of the fast cool down requirements. The cryocooler field is fast developing and the number of applications are growing because of the increasing costs of the cryogens such as Helium and Neon. The first chapter of the book introduces the different types of cryocoolers, their classification, working principles, and their design aspects, and briefly mentions some of the applications of these systems. This introductory chapter is followed by a number of contributions from prominent international researchers, each describing a specific field of application, the cooling requirements and the cryocooler systems employed. These areas of application include gas liquefaction, space technology, medical science, dilution refrigerators, missile systems, and physics research including particle accelerators. Each chapter describes the cooling requirements based on the end use, the approximate cooling load calculations, the criteria for cryocooler selection, the arrangement for cryocooler placement, the connection of the cooler to the object to be cooled, and includes genuine case studies. Intended primarily for researchers working on cryocoolers, the book will also serve as an introduction to cryocooler technology for students, and a useful reference for those using cryocooler systems in any area of application.

The last few years have witnessed a substantial maturing of long life Stirling-cycle cryocoolers built upon the heritage of the flexure-bearing cryocoolers from Oxford University, and have seen the emergence of mature pulse tube cryocoolers competing head-to-head with the Stirling cryocoolers. Hydrogen sorption cryocoolers, Gifford-McMahon cryocoolers with rare earth regenerators, and helium Joule-Thomson cryocoolers have also made tremendous progress in opening up applications in the 4 K to 10 K temperature range. Tactical Stirling cryocoolers, now commonplace in the defense industry, are finding application in a number of cost constrained commercial applications and space missions, and are achieving ever longer lives as they move to linear-drive, clearance-seal compressors. Building on this expanding availability of commercially viable cryocoolers, numerous new applications are being enabled; many of these involve infrared imaging systems, and high temperature superconductors in the medical and communications fields. The vibration sensitivity of many of the infrared and medical imaging applications has led to the recognition that cryocooler-generated vibration and EMI is a critical performance parameter for these applications. In response, advanced closed-loop active vibration control systems have been developed and are being delivered to their first users. Application experiments, designed to explore, troubleshoot and resolve product integration issues, are occurring on an ever widening front, particularly in the fields of infrared imaging and spectroscopy, gamma-ray spectroscopy, and high-temperature superconductor applications. An important lesson is that integrating cryogenic systems requires care and thoughtfulness in a broad range of engineering and scientific disciplines.

Proceedings of the 9th International Conference held in Waterville Valley, New Hampshire, June 25-27, 1996

Composed of papers written by leading engineers and scientists in the field, this valuable collection reports the most recent advances in cryocooler development, contains extensive performance test results and comparisons, and relates the latest experience in integrating cryocoolers into advanced applications.